The present invention relates to passive infrared (PIR) motion detectors of the type used in residential outdoor lighting fixtures, for example, to illuminate a walkway or driveway when a person or automobile approaches. The invention is more particularly directed to electronic circuitry for energizing a light at a dim background level in the absence of motion and at a brighter level in response to motion.
PIR motion detectors are commonly used in conjunction with outdoor light fixtures and indoor light switches to turn on a light in response to a person moving in the field of view monitored by the motion detector. The motion detector typically causes the light to remain on for a pre-set duration after motion has been detected. Thus, for example, when a person enters the motion detector's field of view, a light comes on and remains on typically for five to fifteen minutes. The light is then automatically extinguished at the end of the pre-set period unless further motion is detected. In the earlier motion-activated light fixtures, either the light was on at its full-brightness level or it was off. Thus, at night the area remained dark until motion was detected and then the light only remained on for the pre-set duration after the motion ceased before returning to its dark state. These light fixtures also typically included a daylight sensor for disabling the motion detector during the daytime so that the light would not turn on during daylight hours, as well as a manual override feature by which a user could manually turn the light on at full brightness at any time by toggling a wall switch quickly between the on and off positions.
In a parallel development independent of motion-activated lighting, lighting fixtures providing background illumination at a low level were used in landscape and architectural design to focus attention on such features as walkways and garden paths, trees and prominent shrubbery, statuary and garden art, and ornamental building elements. Such lighting is commonly referred to as accent lighting and typically provides illumination at levels significantly less than full brightness.
The next development was the combination of motion-activated lighting with accent lighting. A number of companies introduced PIR motion detectors that provided for more than one level of illumination. Nippon Ceramic Company, Ltd. introduced a so-called stepped PIR motion detector that provided stepped dimming for use in lighting fixtures. The Nippon motion detector activated the light at full power in response to motion and partially activated the light to an accent level of only 25 percent power in the absence of motion. The daylight sensor disabled the unit in daylight hours so that the accent lighting would turn off automatically in the daytime. Such stepped-dimming PIR motion detecting light fixtures were also available from such companies as Ruud Lighting, Inc., Universal Energy Control, Inc., and Regent lighting Corporation.
An example of electrical circuitry for a stepped dimming motion-activated lighting fixture is disclosed in U.S. Pat. Nos. 5,598,066 and 5,747,93. This circuitry relies on a sensing technique known as zero-crossing detection to control the dimming and has the disadvantage that it is complex and calls for many electronic components, which increases cost, makes greater demands on quality control, and is potentially subject to greater failure rates.